The present invention relates to a headlamp for a motor vehicle using a discharge bulb as a light source, and more particularly to a headlamp for a motor vehicle in which the degree of safety in removing an actuator circuit unit from a lamp body is improved.
Recently, discharge bulbs have been employed for light sources for headlamps because the bulbs are capable of producing light beams of high intensity and they have a long lifetime. Where a discharge bulb is used as a light source, an actuator circuit for causing the discharge bulb to start its discharge and a ballast circuit for causing the discharge bulb to continue a stable discharge must be provided.
FIG. 1 shows a vehicular headlamp of a type previously proposed. A discharge bulb 2 is inserted into a bulb insertion hole la of a reflector 1. An actuator circuit unit 5 is attached to a circular opening portion 4 of a lamp body 3 into which the bulb is removably inserted. A ballast circuit unit 6, mounted to a car body B, is disposed in the vicinity of the light-on circuit unit 5. The actuator circuit unit 5 is connected to the discharge bulb 2 by way of an output cord 5a and a connector 5b. The actuator circuit unit 5 and the ballast circuit unit 6 are constructed such that an actuator circuit and a ballast circuit are assembled into cases, respectively. The two circuits are connected to each other by an output cord 7. The output cord 7 leads from the ballast circuit unit 6. A connector 8 attached to the end of the output cord 7 is removably attached to a connector connection portion 9 of the actuator circuit unit 5 in a simple manner. Reference numeral 5c designates a tubular extended portion fastened to the actuator circuit unit 5. The forward end part of the tubular extended portion 5c is coupled with the circular opening portion 4 in a bayonet fashion. To remove the actuator circuit unit 5 from the circular opening portion 4, the circuit unit 5 (and the extended portion 5c) are rotated along the inner circumferential edge of the circular opening portion 4 in the removal direction.
When the discharge bulb 2 is turned on, a voltage of 85 V (standard value) is applied to the output cord 7 which connects the actuator circuit unit 5 to the ballast circuit unit 6, the output cord 5a for connecting the discharge bulb 2 to the actuator circuit unit 5, and the connector 5b. If the output cord 7 is removed from the actuator circuit unit 5 or the connector 5b is removed from the discharge bulb 2 while the headlamp is being fed with current, the fail-safe circuitry of the ballast circuit will operate to stop the supply of power to the headlamp after approximately 0.7 sec. However, while the headlamp is being fed with current, if the bulb is removed for some reason, a high voltage of approximately 20 KV is induced in the output cord 5a and the connector 5b at the instant the connector 5b is removed from the discharge bulb 2. This high voltage is very dangerous to an operator and can cause a severe electric shock. When the output cord 7 is removed from the actuator circuit unit 5, a voltage of approximately 400 V is induced in the output cord 7. At this voltage level, the operator will not receive an electrical shock unless the metal conductor of the cord 7 is directly touched. Thus, this voltage is not so dangerous to the operator if care is used.
For these reasons, it is the usual practice in changing a light bulb to turn off the power source to stop the supply of electric power to the actuator circuit unit 5 and the output cord 5a before the actuator circuit unit 5 and the connector 5b are removed.
However, it is possible to turn the actuator circuit unit 5 in its removal direction with respect to the circular opening portion 4 while the bulb is still lit. Therefore, there is the possibility that operator may mistakenly remove the actuator circuit unit 5 and the connector 5b while the bulb is powered. This is very dangerous.